Hey there,

 As far as the exams are considered, both of them score to be very similar, if I am not wrong it is 60 questions in 70 minutes for both the exams. The difficulty level is same for both, maybe in a year the kcet questions in one of the subjects P/C/M would be difficult. But on the overview both of them require same type of preparation, Look into the Karnataka PU syllabus and then prepare accordingly. If you are preparing for IIT-JEE and AIEEE, just concentrating on the residual chapters in PU syllabus would be more than sufficient since kcet/ComedK is a lot more easier than JEE.